Still-video equipment produces still-video snapshots of moving or stationary images. In contrast to conventional photographic equipment, the video image or "picture" is captured as digital data on magnetic storage media such as a floppy disk.
The specific problem to which the invention is applicable is the reproduction of still-video images captured on magnetic media in hard copy form.
Still-video systems can transmit still-video (or freeze-frame) images, in color or black and white, over telecommunications facilities, and then print hard copy reproductions of those images. Specific examples include: (a) wire photography; (b) still-video peripheral equipment; and (c) specialty products.
Wire photography, and its extension radio photography, have long been used by the news media. The most common form involves an input device that converts photographs into encoded signals for communication over telecommunications facilities or radio. At the receiving end, reproducing equipment reconverts the encoded image signals by exposing photographic film or other sensitized paper. The term facsimile is often used with these products.
Still-video equipment has recently become available from such vendors such as Canon and Sony, and is again primarily used by the television and print media, although applications are expanding rapidly in such areas as insurance investigation and real estate. A still-video camera (or camcorder) captures a full-color still-video image that can be reproduced using a special video printer that converts the still-video image data into hard copy form. For applications requiring communication of the still-video image, transmit/receive units are available that transmit/receive video signals--the signal begins and ends as a video image, and proprietary transmission techniques are typically used for communication.
An example of a specialty product is the PhotoPhone from Image Data Corporation. This product has a video camera, display and storage facility in a terminal package. One terminal can send a real-time or stored still-video image to another for display or storage, or printing on special video printers. The signal begins and ends as a video image, and may use standard or proprietary transmission techniques.
Another example of a specialty product is the special peripheral equipment available for personal computers (PCs) that enable the input/output, storage and processing of still-video images in digitized formats. For instance, the Canon PV-540 is a floppy disk drive that uses conventional still-video disks, digitizing a still-video image using a conventional format, and communicating with the PC through a standard computer I/O port.
Most PC communication utilities for still-video images are based on one of a number of conventional data record formats. Once an image is stored in one of these formats as a single file under the PC operating system, it can be mailed by E-mail or communicated by any of the common communications programs to another PC. The still-video image file can be transferred to photographic film, or printed on conventional laser printers.
Laser printers and some other image output equipment often use a half-tone format that produces a half-tone photographic image. More recently, standard facsimile equipment has been enhanced for transmitting half-tone images. In addition, for personal computers, facsimile interface products are available for digitally capturing a complete still-video picture from a video source, and, through a software transformation, creating a half-tone image suitable for transmission to a facsimile machine.
These half-tone images are created by arranging the conventional facsimile dot-pattern output into half-tone pixels--dot matrix areas, or dot clusters, that contain a predetermined number dots. A half-tone picture is composed of half-tone pixels, each of which can be varied from white to black by appropriately selecting the number of dots that are included within a pixel.
Producing optimum image quality in half-tone is considered an "art" in the publishing business. Many parameters are manipulated, including shades of grey, dots per inch, the shape of the dots, the arrangement of the dot dither (a smoothing technique), screen angle (the angular relationship of the dots to each other), and transfer functions (changing the density at various gray levels to compensate for ink retention). Half-tone resolution in newspapers have "rulings" of from 55 to 150 lines per inch, while magazine parameters commonly fall between 120 to 150 lines per inch.
In currently available equipment for producing half-tone reproductions of still-video images, an entire still-video image is stored as an intermediate digitized grey-scale image frame prior to being converted to half-tone data for producing a hard copy output. Such an intermediated storage stage is disadvantageous in a number of respects.
Cost factors can become significant if additional components, such as memory chips and supporting logic, are required (thereby also increasing power consumption). In particular, the requirement for digital memory to store an intermediate still-video half-tone frame significantly increases the size of the resulting electronics including, if portability is desired, battery storage. Also, intermediate digital storage requires an intermediate grey-scale digitization that introduces irregularity into subsequent image transformations, with resulting loss of resolution and image quality degradation.
In particular, in the case of facsimile printing that also involves a digital format in the form of the printing dots, the image patterns from the intermediate grey-scale image data can result in beat-frequencies or super patterns when merged with the facsimile dot formats. These extra patterns can cause significant image quality degradation without substantial electronic filtering. Such filtering requires extra components and can, itself, degrade resolution or image quality.
Accordingly, a need exists for still-video conversion equipment that can convert still-video image data in real-time for hard copy output without the need for creating or storing an intermediate still-video image frame.